1	CS110 Lecture 11 Thursday, March 4, 2004 Announcements hw5 available, due next Thursday Exam answers posted Agenda exam results arrays better Banks and BankAccounts ArrayLists
2	Exam results Range: (<30) – (100/102) 50 isn’t wonderful, but it’s OK (passing) Answers posted – no questions answered until you have studied them Check my addition, please (both ways!) Letter grade ranges on next slide are for exam only, don’t take hw into account
3
4	Array Simplest Java object for managing a list array syntax uses square brackets [] several ways See ArrayDemo.java in JOI Study CommandLineArgsDemo.java (JOI) Study ArrayDemo2.java (handout)
5	Command line arguments in Java public static void main(String[] args) args is a parameter for the main method The declaration says it’s an array of String objects Its contents are the words on the command line after java ClassName Argument array can have any name you wish args is conventional old C programmers may call it argv
6	Command line arguments in Java class CommandLineArgsDemo public static void main( String[] args ) { for (int i = 0; i < args.length; i++){ System.out.println('\|'+args[i]+'\|'); } } %> java CLID message is "hello, world " \|message\| \|is\| \|hello, world \| Experiment with %> java Bank -e
7	ArrayDemo2.java Array practice, some idioms/tricks converting Strings to ints finding sum, maximum and minimum > java ArrayDemo2 -1 -2 -3 4 5 total: 3 maximum: 5 minimum: -3
8	Two dimensional arrays, nested for loops (from Screen.java) 24 private char[][] pixels; 45 public void clear() 46 { 47 for (int x = 0; x < width; x++) { for ( int y = 0; y < height; y++ ) { pixels[x][y] = BLANK; } } }
9	arrays are Objects (even though there is no Array class) … The square brackets provide the special syntax for sending an array a message Created with new Size is determined at creation time but not at declaration time myArray[i] refers to the value stored at index i (which must be an integer) Stored values may be primitive (in the box) or a reference to an object (an arrow) but all values must have the same type
10	array summary declare: Type[ ] myArray; // Type is class name, or primitive create: myArray = new Type[ size ]; put: myArray[ index ] = …; get: Type x = myArray[ index ]; myArray[ index ].message(); length: myArray.length; range: 0,1,…, myArray.length-1
11	A better Bank (Version 4)... Maintains a list of BankAccounts Allows banker to create new accounts while the Bank is open Keeps track of the total balance of all the accounts in it, and of the total number of transactions performed by its accounts
12	Arrays in the better Bank Bank.java (version 4) uses an array Declare field accountList of type “array of BankAccounts” (line 32) private BankAccount[] accountList ; Create the array, ready to hold 3 Items (60) accountList = new BankAccount[NUM_ACCOUNTS];
13	An array for 3 BankAccounts // fill array on lines 66-68 accountList [0] = new BA( 0, this); accountList [1] = new BA(100, this); accountList [2] = new BA(200, this); Improved BankAccount object has a field to hold a reference to the Bank it belongs to (more later)
14	boxes and arrows for arrays
15	Improved BankAccount Private fields (all have getter methods) int balance; int transactionCount; Bank issuingBank; Constructor public BankAccount(int initialBalance, Bank issuingBank) { this.issuingBank = issuingBank; this.deposit(initialBalance); }
16	Improved Bank banker commands create new account (for hw5) report on totals deal with a customer deposit withdraw get balance transfer
17	Bank and BankAccount cooperate public int deposit( int amount ) { this.incrementBalance( amount ); this.countTransaction(); return amount ; } public void incrementBalance(int amount) { balance += amount; this.getIssuingBank(). incrementBalance( amount ); }
18	A Bank object and its fields
19	ArrayList A Collection class in the Java API Like an array: stores elements at positions 0,1,… Can grow as needed! Unlike an array in other ways too stores only objects (not primitive types) can store different kinds of objects simultaneously (so you must cast when retrieving) send messages instead of using [ ] for access Read ArrayListDemo.java
20	ArrayList API can store: any Object, not primitive types declaration: ArrayList myList creation: myList = new ArrayList( ) put at end: myList.add( obj ) put at index: myList.add( index, obj ) moves later entries down the list get: (Type)myList.get( index ) cast to proper Type after get replace: myList.set( index, obj ) remove: myList.remove( index ) size: myList.size( ) looping: for( ; ; )11
21	Boxes and arrows for ArrayList
22	hw5 array practice (sorting) ArrayList practice: modify Bank.java so that it uses an ArrayList of BankAccounts instead of an array BankAccounts have numbers 0, 1, 2, … Banker can open as many accounts as she likes!